FR3141246A1 - IN-SITU FOUR-POINT BENDING TEST OF AN ANGLE - Google Patents

Abstract

Four-point in situ bending test machine (30) for measuring the mechanical properties of a specimen (10) in the form of an angle iron, comprising: - two lower supports (26) which are located in a first horizontal plane (P1) and which are spaced from each other by a first predetermined distance (D1), - two upper supports (28) which are located in a second horizontal plane (P2) located above the first plane (P2) and which are spaced from each other by a second predetermined distance (D2) less than the first distance (D1), characterized in that it comprises a frame (32) fixed in translation and a movable part (34) in translation, the lower supports (26) being rigidly connected to the frame (32) which is intended to be located under the specimen (10), and the upper supports (28) being connected to the movable part (34) which is also intended to be located under the test piece (10). Figure for abstract: Figure 2

Description

IN-SITU FOUR-POINT BENDING TEST OF AN ANGLE Technical field of the invention

The present invention relates to an in situ four-point bending test machine and method for measuring the out-of-plane mechanical properties of a material from an angle-shaped specimen, as well as a tomographic installation comprising this machine. .

Technical background

In hot areas of aircraft engines, ceramic matrix composites (whose acronym is CMC – such as SiC/SiC) are good candidates to replace superalloys. The three-dimensional armor of the CMC is designed to optimize their mechanical strength in service. It depends on the geometry of the parts and their thermomechanical loading. The mesostructure then includes complex zones, for example at bends or junctions. A good understanding of the thermomechanical behavior in these zones is necessary to model, size and certify aeronautical parts.

Determining the out-of-plane properties of CMC materials (and the damage kinetics) is difficult to achieve because their thicknesses are thin. However, these properties are essential for part sizing. There is therefore a need to determine the out-of-plane properties (and damage kinetics) of CMC materials (Oxide/Oxide, CMC carbide, etc.) using an in-situ 4-point angle bending test under tomography.

To date, the direction 3 mechanical properties of fine material are determined either by direction 3 traction on a glued disc (ILT: Interlaminar tensile test ) or by 4-point angle bending test.

Sense 3 traction (ILT) consists of cutting discs of known diameter (e.g.: 25mm) and gluing their two faces to heels (e.g.: aluminum). These heels are then inserted into a traction machine. The breaking force divided by the surface area makes it possible to determine the breaking stress in direction 3. This test leads to a high variability of the breaking stresses which is detrimental for the determination of the admissible stresses in the material. Improvements have been proposed in the corresponding standards without much reduction in dispersion.

The 4-point angle bending tests make it possible to stress the “corner” zone in tension direction 3. This test makes it possible to determine the breaking stress with less dispersion. However, current technology testing machines are not suitable for carrying out tomograph testing. In fact, these machines are relatively bulky and the angle is hidden by the machine during the tests. It is therefore difficult or even impossible to carry out a tomography of the angle during a test.

The present invention proposes a simple, effective and economical improvement which makes it possible to optimize the size of the testing machine and allow its use with a tomographic installation.

The invention relates to an in situ four-point bending testing machine for measuring the mechanical properties of a specimen in the form of an angle iron, this specimen comprising two wings connected at right angles and comprising an interior surface and an exterior surface, the machine comprising:

- two lower supports which are located in a first horizontal plane and which are spaced apart from each other by a first predetermined distance, the test piece being intended to be positioned on these two lower supports so that these supports are at the contact of the interior surface of the test piece, respectively on the two wings, and

- two upper supports which are located in a second horizontal plane located above the first plane and which are spaced from each other by a second predetermined distance less than the first distance, these two upper supports being intended to be in contact with the exterior surface of the test piece, respectively on the two wings,

characterized in that it comprises a frame fixed in translation and a part movable in translation relative to the frame, the lower supports being rigidly connected to the frame which is intended to be located under the specimen, and the upper supports being connected to the movable part which is also intended to be located under the test piece and which is movable in the vertical direction.

The machine according to the invention is thus configured to facilitate its use in a tomographic installation. Indeed, the arrangement of the frame and the movable part under the specimen allows the specimen to be located at the upper end of the machine and to be easily accessible and visible by the beam of a ray generator X of a tomographic installation for example.

The machine according to the invention may comprise one or more of the following characteristics, taken in isolation from each other, or in combination with each other:

- the frame comprises a lower base and two upper posts, these posts being vertical and spaced apart from each other, the lower ends of the posts being connected to the base and their upper ends being connected to said lower supports;

- the frame further comprises a rotating support plate around a vertical axis, the base being fixed on this support plate;

- the movable part comprises a U-shaped element comprising vertical branches spaced from one another and connected by a lower bridge, the upper ends of these branches being connected to said upper supports;

- the U-shaped element comprises two pairs of branches, a first pair of branches being located on a first side and connected to a first of the upper supports, and a second pair of branches being located on a second side and connected to a second of the upper supports, the test piece being intended to pass between the branches of the first pair and between the branches of the second pair;

- the lower bridge of the U-shaped element is connected to at least one vertical guide rod;

- the or each guide rod is configured to slide in an orifice or a notch in the frame;

- the lower and upper supports are formed by cylindrical surfaces of cylindrical fingers oriented horizontally;

-- the test piece is intended to be positioned so that its connecting edge of the wings is horizontal;

- said mobile part is equipped with a force sensor;

-- the surfaces of the test piece have an L or dihedral shape.

The present invention also relates to an in situ four-point bending test installation under tomography for measuring the mechanical properties of a test piece in the form of an angle iron, this installation comprising an X-ray generator, a plane detector oriented vertically and connected to a computer system for data acquisition and processing, and a machine as described above located between the X-ray generator and the plane detector.

Good knowledge of boundary conditions and damage mechanisms via tomography makes it possible to reduce measurement uncertainties and provides added value for understanding the behavior of the part.

The invention further relates to an in situ four-point bending test method for measuring the mechanical properties of a specimen in the form of an angle iron, this method being implemented by means of a machine or installation such as described above, the specimen being made of composite material with a ceramic matrix.

The method comprises for example a step of moving in translation the fixed part with respect to said frame. The method comprises for example a step of rotating the plate around its axis.

Brief description of the figures

Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which:

there is a schematic view of an in situ four-point bending testing machine, according to the prior art,

there is a schematic perspective view of an in situ four-point bending testing machine according to one embodiment of the invention,

there is another schematic perspective view of the machine of the ,

there is a schematic perspective view of an in situ four-point bending testing machine according to an alternative embodiment of the invention,

there is another schematic perspective view of the machine of the ,

Figures 6a and 6b are schematic views of a test piece and the supports of a machine, and illustrate different positions of the upper supports,

there is a very schematic perspective view of a tomographic installation according to the invention,

Figures 8a and 8b are views similar to Figures 6a and 6b and further show an X-ray beam during tomography,

Figures 9a and 9b are schematic top views of a machine and show a rotating support plate of this machine, and

Figures 10a and 10c are images obtained by tomography of specimens which were subjected to four-point bending tests in situ.

Detailed description of the invention

We first refer to the which shows the general principle of a four-point bending test in situ according to the prior art.

This type of test makes it possible to measure the mechanical properties of a test piece 10 in the shape of an angle iron.

A test piece 10 of this type comprises two wings 12 connected at right angles and comprising an interior surface 14 and an exterior surface 16. Each of these surfaces 14, 16 has a general L-shaped or dihedral shape.

This test is the subject of an ASTM standard whose reference is D6415/D6415M. Those skilled in the art are aware of this standard which will therefore not be detailed in what follows.

The test is carried out by means of a machine 20 which is schematically represented by two parts 22, 24 in the , each of these parts 22, 24 comprise or carry supports 26, 28 on the test piece 10.

The supports 26, 28 are four in number so as to form the four support points of the test. There are two lower supports 26 and two upper supports 28. The two lower supports 26 are arranged under the specimen 10 and intended to bear on its interior surface 14. The two upper supports 28 are arranged on the specimen 10 and are intended to rest on its exterior surface 16.

Part 22 is a lower part which is located under the test piece 10 and which carries the lower supports 26. The lower supports 26 are located in a first horizontal plane P1 and are spaced apart from each other by a first distance D1 predetermined.

The specimen 10 is positioned on the supports 26 so that these supports are in contact with the interior surface 14 of the specimen, respectively on the two wings 12.

Part 24 is an upper part which is located above the test piece 10 and which carries the upper supports 28. The upper supports 28 are located in a second horizontal plane P2 which is located above the first plane P1, and are spaced from each other by a second predetermined distance D2 which is less than the first distance D1.

The upper supports 28 are in contact with the exterior surface 16 of the specimen 10, respectively on the two wings 12.

In the test position, the test piece 10 is positioned so that its connecting edge or corner of the wings 12 is preferably horizontal.

As we see in the , the parts 22, 24 are moved in vertical translation towards each other (arrows F1 and F2) so that the supports 26, 28 exert a bending force on the specimen 10.

Figures 2 and 3 illustrate a first embodiment of a testing machine 30 according to the invention.

The particularity of this machine 30 is that it comprises a frame 32 fixed in translation and a part 34 movable in translation relative to the frame 32 unlike the aforementioned prior technique in which the two parts 22, 24 are movable.

The lower supports 26, similar to those described above, are rigidly connected to the frame 32 which is intended to be located under the test specimen 10.

The upper supports 28, similar to those described above, are connected to the movable part 34 which is also intended to be located under the test piece 10 and which is movable in the vertical direction (arrow F3).

As mentioned in the above, this configuration of the machine 30 allows the test piece 10 to remain accessible and visible by a tomograph.

The frame 32 comprises a lower base 36 and two upper posts 38.

The posts 38 are vertical and spaced from one another. The lower ends of the posts 38 are connected to the base 36 and their upper ends are connected to the lower supports 26. In the example shown, the lower supports 26 are formed by cylindrical surfaces of cylindrical fingers oriented horizontally. These fingers have a predetermined diameter. They are preferably made of a material with a low level of X-ray absorption and which can withstand high temperatures.

The frame 32 further comprises a support plate 40 rotating around a vertical axis A. The base 36 is fixed on this support plate 40 which can have a generally circular or disc shape.

Part 34 is movable in translation in the vertical direction preferably along the axis A of rotation of the support plate 40.

Part 34 comprises a U-shaped element 42 comprising vertical branches 44, 46 spaced from one another or from each other and connected by a lower bridge 48.

The upper ends of the branches 44, 46 are connected to the upper supports 28. In the example shown, the upper supports 28 are formed by cylindrical surfaces of cylindrical fingers oriented horizontally. These fingers have a predetermined diameter. They are preferably made of a material with a low level of X-ray absorption and which can withstand high temperatures.

In the example shown, the U-shaped element 42 comprises two pairs of branches, the branches 44a, 44b of a first pair being located on a first side and connected to a first of the upper supports 28, and the branches 46a, 46b of a second pair being located on a second side and connected to a second of the upper supports 28.

As we see in the , the test piece 10 is intended to pass between the branches 44a, 44b of the first pair and between the branches 46a, 46b of the second pair.

The lower bridge 48 of the U-shaped element 42 is connected to at least one vertical guide rod 50. The or each rod 50 is configured to slide in an orifice or a notch of the frame 32.

As we see in the , the U-shaped element 42 is arranged between the posts 38 and is able to be moved along the axis A between these posts 38.

There are two of these rods 50 in the example shown. They are parallel to axis A and at a distance from each other. They pass through holes in the base 36 and the support plate 40.

The upper ends of the rods 50 are connected to the U-shaped element and their lower ends are located under the frame 32 and in particular the support plate 40, and are configured to be connected to an actuator 52.

The actuator 52 is for example of the hydraulic type or of the motor/reducer type with endless screw, although this aspect is not limiting.

The mobile part 34 is preferably equipped with a force sensor 53 (placed for example in series) making it possible to record the force transmitted by the actuator 52

Figures 4 and 5 illustrate a variant embodiment of the machine 30. This variant differs from the previous embodiment essentially in that the frame 32 is less bulky and includes a base 36 comprising notches for guiding the rods 50 of the movable part 34.

Figures 6a and 6b show that distance D1, distance D2 or distances D1 and D2 can be adjusted.

In Figure 6a, the lower supports 26 are at the distance D1 from each other and the upper supports 28 are at the distance D2 from each other. In Figure 6b, the upper supports 28 have been further apart from each other and are at the distance D2' greater than D2.

There shows a tomographic installation 60 comprising a machine 30 as described in the above.

The machine 30 is represented in a simplified manner in the with its support plate 40 movable in rotation around the axis A, and its guide rods 50.

The installation 60 further comprises a tomograph or X-ray generator 62 and a plane detector 64 oriented vertically and connected to a computer system 66 for data acquisition and processing.

The generator 62 produces a beam 68 of X-rays which passes through the test tube 10 and which is projected onto the plane detector 64.

Figures 8a and 8b show that the machine 30 is particularly designed not to disturb the propagation of the beam 68. The upper supports 28 are for example moved to avoid being in the field of this beam 68. This makes it possible to clear the beam or the top of the test piece 10 and to limit the “noise” generated by the supports.

Figures 9a and 9b show that the overall dimensions of the assembly must be reduced as much as possible in order to bring the test assembly as close as possible to the X-ray source and thus obtain the best possible resolution for the images, whatever the the orientation of the assembly (red circumscribed circle).

Finally, Figures 10a to 10c are images of a test piece 10 obtained by the tomographic installation 60 during an in situ four-point bending test.

The images are taken during the same test, at three different times.

The first image at time t1 (corresponding for example to a first loading) shows the initiation of a crack in zone Z1 ( ^1st damage). The second image at time t2 (corresponding for example to a second loading) shows propagation of the crack in zone Z1. The third at time t3 (corresponding for example to a loading to rupture) shows delaminations in zone Z1 and in other zones Z2.

In yet another variant not shown, the test could be carried out hot, that is to say at high temperature. In this case, the test piece could be heated directly by resistivity or induction. The test tube would then be heated by the Joule effect by passing an electric current.

Claims (11)

Four-point in situ bending testing machine (30) for measuring the mechanical properties of a specimen (10) in the form of an angle iron, this specimen (10) comprising two wings (12) connected at right angles and comprising an interior surface (14) and an exterior surface (16), the machine (30) comprising:
- two lower supports (26) which are located in a first horizontal plane (P1) and which are spaced from each other by a first predetermined distance (D1), the test piece (10) being intended to be positioned on these two lower supports (26) so that these supports are in contact with the interior surface (14) of the test piece (10), respectively on the two wings (12), and
- two upper supports (28) which are located in a second horizontal plane (P2) located above the first plane (P2) and which are spaced apart from each other by a second predetermined distance (D2) less than the first distance (D1), these two upper supports (28) being intended to be in contact with the exterior surface (16) of the specimen (10), respectively on the two wings (12),
characterized in that it comprises a frame (32) fixed in translation and a part (34) movable in translation relative to the frame (32), the lower supports (26) being rigidly connected to the frame (32) which is intended to be located under the specimen (10), and the upper supports (28) being connected to the movable part (34) which is also intended to be located under the specimen (10) and which is movable in the vertical direction. Machine (30) according to claim 1, in which the frame (32) comprises a lower base (36) and two upper posts (38), these posts (38) being vertical and spaced apart from each other, the ends lower ends of the posts (38) being connected to the base (36) and their upper ends being connected to said lower supports (26). Machine (30) according to claim 2, in which the frame (32) further comprises a support plate (40) rotatable around a vertical axis (A), the base (36) being fixed on this support plate (40). ). Machine (30) according to one of the preceding claims, in which the movable part (34) comprises a U-shaped element (42) comprising vertical branches (44, 46) spaced from one another and connected by a bridge lower (48), the upper ends of these branches (44, 46) being connected to said upper supports (28). A machine (30) according to claim 4, wherein the U-shaped member (42) comprises two pairs of legs (44a, 44b, 46a, 46b), a first pair of legs (44a, 44b) being located on a first side and connected to a first of the upper supports (28), and a second pair of branches (46a, 46b) being located on a second side and connected to a second of the upper supports (28), the test piece (10) being intended to pass between the branches (44a, 44b) of the first pair and between the branches (46a, 46b) of the second pair. Machine (30) according to claim 4 or 5, in which the lower bridge (48) of the U-shaped element is connected to at least one vertical guide rod (50). Machine (30) according to claim 6, wherein the or each guide rod (50) is configured to slide in an orifice or notch in the frame (32). Machine (30) according to one of the preceding claims, in which the lower (26) and upper (28) supports are formed by cylindrical surfaces of horizontally oriented cylindrical fingers. Machine (30) according to one of the preceding claims, in which said movable part (34) is equipped with a force sensor (53). Installation (60) for in situ four-point bending test under tomography for measuring the mechanical properties of a specimen (10) in the form of an angle, this installation (60) comprising an X-ray generator (62), a plane detector (64) oriented vertically and connected to a computer system (66) for data acquisition and processing, and a machine (30) according to one of the preceding claims located between the X-ray generator (62) and the plane detector (64). Four-point bending test method in situ for measuring the mechanical properties of a specimen (10) in the form of an angle iron, this method being implemented by means of a machine (30) according to one of claims 1 to 9 or an installation (60) according to claim 10, the specimen (10) being made of ceramic matrix composite material.